Darwin's Boulders

Charles Darwin visited Cwm Idwal in 1831, and observed that the large scattered boulders at Llyn Idwal lake contained marine seashells. He realised that the rocks must have formed within an ancient ocean, and therefore had been later uplifted to the surface by forces within the Earth’s crust. He later found that the landscape of Cwm Idwal was shaped by glaciers, at a time when Wales was far colder than it is today, more than 10,000 years ago.